U.S. patent application number 12/506402 was filed with the patent office on 2010-06-10 for binder compositions and membrane electrode assemblies employing the same.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Ssu-Tai LIN, Jing-Pin PAN, Tsung-Hsiung WANG.
Application Number | 20100143767 12/506402 |
Document ID | / |
Family ID | 42231438 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100143767 |
Kind Code |
A1 |
WANG; Tsung-Hsiung ; et
al. |
June 10, 2010 |
BINDER COMPOSITIONS AND MEMBRANE ELECTRODE ASSEMBLIES EMPLOYING THE
SAME
Abstract
Binder composites for membrane electrode assemblies and membrane
electrode assemblies employing the same are provided. The binder
composition includes a solvent, a hyper-branched polymer and a
polymer with high ion conductivity, wherein the hyper-branched
polymer and the polymer with high conductivity of hydronium are
distributed uniformly over the solvent, and the hyper-branched
polymer has a DB (degree of branching) of more than 0.5.
Inventors: |
WANG; Tsung-Hsiung; (Dali
City, TW) ; PAN; Jing-Pin; (Hsinchu Hsien, TW)
; LIN; Ssu-Tai; (Nantou County, TW) |
Correspondence
Address: |
LOWE HAUPTMAN HAM & BERNER, LLP
1700 DIAGONAL ROAD, SUITE 300
ALEXANDRIA
VA
22314
US
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
Hsinchu
TW
|
Family ID: |
42231438 |
Appl. No.: |
12/506402 |
Filed: |
July 21, 2009 |
Current U.S.
Class: |
429/483 ;
252/500; 252/519.33; 525/417 |
Current CPC
Class: |
Y02E 60/50 20130101;
C08L 81/06 20130101; H01B 1/24 20130101; C08L 101/005 20130101;
C08L 2205/02 20130101; H01M 10/0525 20130101; H01B 1/122 20130101;
Y02E 60/10 20130101; H01M 2008/1095 20130101; C08G 73/122 20130101;
C08L 71/00 20130101; H01M 4/8668 20130101; C08L 71/12 20130101;
C08G 73/124 20130101; C08G 2650/40 20130101; H01M 8/16 20130101;
C08L 79/085 20130101; C08L 71/00 20130101; C08L 2666/20 20130101;
C08L 71/12 20130101; C08L 2666/20 20130101; C08L 79/085 20130101;
C08L 2666/14 20130101; C08L 81/06 20130101; C08L 2666/20
20130101 |
Class at
Publication: |
429/40 ; 525/417;
252/500; 252/519.33 |
International
Class: |
H01M 4/00 20060101
H01M004/00; C08G 73/10 20060101 C08G073/10; H01B 1/20 20060101
H01B001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2008 |
TW |
97147619 |
Claims
1. A binder composition for a membrane electrode assembly,
comprising a solvent; a hyper-branched polymer, wherein the
hyper-branched polymer has a DB (degree of branching) of more than
0.5; and a polymer with high ion conductivity, wherein the
hyper-branched polymer and the polymer with high ion conductivity
are distributed uniformly over the solvent.
2. The binder composition as claimed in claim 1, wherein the
hyper-branched polymer comprises a polymer prepared by polymerizing
a bismaleimide-containing compound with a barbituric acid.
3. The binder composition as claimed in claim 2, wherein the molar
ratio of the bismaleimide-containing compound and barbituric acid
is 20:1 to 1:5.
4. The binder composition as claimed in claim 2, wherein the molar
ratio of the bismaleimide-containing compound and barbituric acid
is 5:1 to 1:2.
5. The binder composition as claimed in claim 2, wherein the
bismaleimide-containing compound comprises substituted or
unsubstituted bismaleimide monomer or substituted or unsubstituted
bismaleimide oligomer.
6. The binder composition as claimed in claim 2, wherein the
bismaleimide-containing compound comprises ##STR00007##
7. The binder composition as claimed in claim 1, wherein the
hyper-branched polymer is in an amount of 5-30 parts by weight,
based on 100 parts by weight of the hyper-branched polymer and the
polymer with high ion conductivity.
8. The binder composition as claimed in claim 1, wherein the
hyper-branched polymer is in an amount of 10-25 parts by weight,
based on 100 parts by weight of the hyper-branched polymer and the
polymer with high ion conductivity.
9. The binder composition as claimed in claim 1, wherein the
polymer with high ion conductivity comprises Nafion, sulfonated
poly(ether ether ketone)(s-PEEK), sulfonated polyimides (s-PI),
phosphoric acid/polybenzimidazole polymer (p-PBI), sulfonated
poly(phenylene oxide) (s-PPO), sulfonated poly(arylene ether
sulfone) (s-PES), or sulfonated
poly(4-phenoxybenzoyl-1,4-phenylene) (s-PPBP).
10. The binder composition as claimed in claim 1, wherein the
solvent comprises .gamma.-butyrolactone (GBL),
1-methyl-2-pyrrolidinone (NMP), dimethylacetamide (DMAC),
N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO),
dimethylamine (DMA), tetrahydrofuran (THF), methyl ethyl ketone
(MEK), propylene carbonate (PC), water, isopropyl alcohol (IPA), or
combinations thereof.
11. The binder composition as claimed in claim 1, further
comprising a conductive material.
12. The binder composition as claimed in claim 1, wherein the
conductive material comprises organic conductive material,
organic-inorganic conductive material, inorganic conductive
material, metal material, organic-metal material, or
inorganic-metal material.
13. The binder composition as claimed in claim 1, wherein the
conductive material comprises carbonaceous material, lithium-cobalt
oxide, lithium-manganese oxide, lithium-nickel oxide,
lithium-cobalt-nickel oxide, lithium-cobalt-nickel-manganese oxide,
or lithium-iron-phosphorus oxide.
14. The binder composition as claimed in claim 1, further
comprising a catalyst.
15. The binder composition as claimed in claim 14, wherein the
catalyst comprises platinum, ruthenium, platinum-ruthenium alloy,
platinum-tin alloy, platinum-tungsten alloy, or platinum-molybdenum
alloy.
16. The binder composition as claimed in claim 1, wherein the
binder composition is used to make a proton exchange membrane
adhere to an electrode.
17. The binder composition as claimed in claim 1, wherein the
binder composition is used to make a catalyst layer adhere to an
electrode.
18. A membrane electrode assembly, comprising: a catalytic anode; a
catalytic cathode a proton exchange membrane disposed between the
catalytic anode and the catalytic cathode; and an adhesive layer
for binding the catalytic anode to the proton exchange membrane and
the catalytic cathode to the proton exchange membrane, wherein the
adhesive layer comprises the binder composition as claimed in claim
1.
19. The membrane electrode assembly as claimed in claim 18, wherein
the membrane electrode assembly is applied in fuel cells, Li-ion
cells, or biocells.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Taiwan Patent Application No. 97147619,
filed on Dec. 8, 2008, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a binder composition and membrane
electrode assemblies employing the same, and more particularly to a
binder composition for high temperature conductivity and membrane
electrode assemblies employing the same.
[0004] 2. Description of the Related Art
[0005] Fuel cells are well known and are commonly used to produce
electrical energy by means of electrochemical reactions. Compared
to conventional power generation apparatuses, fuel cells have
advantages of causing less pollution, generating less noise,
increased energy density and higher energy conversion efficiency.
Fuel cells can be used in portable electronic products, home-use or
plant-use power generation systems, transportation vehicles,
military equipment, space industry application, large-sized power
generation systems, etc.
[0006] For example, in the case of a proton exchange membrane fuel
cell (PEMFC), hydrogen is supplied to an anode and an oxidation
reaction occurs in the presence of an anode catalyst layer, thus
protons and electrons are generated. The protons reach the cathode
through the proton exchange membrane. Meanwhile, in the cathode,
electrons from the anode via the external circuit are reduced to
oxygen supplied to the cathode and protons by reduction, producing
water.
[0007] FIG. 1A shows an exploded view of conventional fuel cell 10
with a membrane electrode assembly, and FIG. 1B shows a
cross-section view of FIG. 1A. As shown in FIGS. 1A and 1B, the
conventional fuel cell 10 can comprise a membrane electrode
assembly 12 comprising a catalytic anode film 121, a proton
exchange membrane 122, and a catalytic cathode film 123, wherein a
binder composition 124 can be used to combine the catalytic anode
film 121 and the proton exchange membrane 122, and/or the catalytic
cathode film 123 and the proton exchange membrane 122. The
conventional fuel cell 10 further comprises a bipolar plate 13 and
two end electrode plates 11 for connection, wherein the bipolar
plate 13 and the end electrode plates 11 comprises gas passages 111
and 131 for conducting hydrogen and oxygen into the membrane
electrode assembly 12.
[0008] In general, conventional binder compositions employed by
membrane electrode assemblies comprise Nafion (manufactured by E.
I. Du Pont de Nemours & Co.) as main component. The Nafion has
adequate physical properties, chemical properties, and proton
conductivity, but some deficiencies exist when used as a main
component of binder compositions.
[0009] To begin, the Nafion-based binder composition exhibits
swelling deformation in the present of aqueous solvent, resulting
in difficulties for precision control during coating processes.
[0010] Further, under relatively high temperatures (>80.degree.
C.), Nafion is apt to softening and may be further induced to
change phases, resulting in reduction of proton mobility
efficiency. Additionally, under relatively low temperatures
(<80.degree. C.), the Nafion exhibits inferior CO tolerance,
resulting in reduction of catalyst efficiency and decrease of the
operating lifespan of fuel cells.
[0011] Moreover, for Nafion-based binder compositions, required
water management is difficult to control. Inefficient water
management may lead to an anode becoming prone to drying and the
cathode to flooding, resulting in oxygen not being able to contact
the surface of the catalyst, thus limiting proton transport.
[0012] Additionally, when operating in a temperature of more than
100.degree. C., Nafion-based binder compositions exhibit inferior
proton mobility, thus, structural deterioration may occur due to
the poor water retention coefficient thereof.
[0013] Accordingly, a novel binder composition for membrane
electrode assemblies to replace conventional Nafion-based binder
compositions is required.
BRIEF SUMMARY OF THE INVENTION
[0014] An exemplary embodiment of a binder composition for a
membrane electrode assembly includes a solvent. A hyper-branched
polymer and a polymer with high ion conductivity are distributed
uniformly over the solvent, wherein the hyper-branched polymer has
a DB (degree of branching) of more than 0.5.
[0015] In an embodiment of the invention, the hyper-branched
polymer comprises a polymer prepared by polymerizing a
bismaleimide-containing compound with a barbituric acid.
[0016] An exemplary embodiment of a membrane electrode assembly
includes a catalytic anode and a catalytic cathode. A proton
exchange membrane is disposed between the catalytic anode and the
catalytic cathode. An adhesive layer is formed for binding the
catalytic anode to the proton exchange membrane and the catalytic
cathode to the proton exchange membrane, wherein the adhesive layer
comprises the aforementioned binder composition of the invention.
In embodiments of the invention, the membrane electrode assembly
can be applied in fuel cells, Li-ion cells, or biocells.
[0017] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0019] FIG. 1A is an exploded view of a conventional fuel cell with
a membrane electrode assembly.
[0020] FIG. 1B is a cross section of the conventional fuel cell
with a membrane electrode assembly as shown in FIG. 1A.
[0021] FIGS. 2A and 2B are partial schematic drawing of membrane
electrode assemblies with the adhesive layer made of the binder
composition according to embodiments of the invention.
[0022] FIG. 3 is a partial schematic drawing of the main
configuration of the adhesive layers disclosed in the membrane
electrode assemblies of FIG. 2A or FIG. 2B.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is best determined by reference to the appended claims.
[0024] The binder composition for membrane electrode assemblies
providing by embodiments of the invention comprises a
hyper-branched polymer and a polymer with high ion conductivity,
wherein the hyper-branched polymer and the polymer with high ion
conductivity are distributed uniformly over a solvent.
[0025] The hyper-branched polymer according to the invention has a
degree of branching (DB) of more than 0.5. The degree of branching
(DB) is defined as the average fraction of branching groups per
molecule, i.e., the ratio of terminal groups plus branched groups
to the total number of terminal groups, branched groups, and linear
groups. The degree of branching is expressed mathematically as
follows:
DB=(.SIGMA.D+.SIGMA.T)/(.SIGMA.D+.SIGMA.L+.SIGMA.T)
[0026] where D represents the number of dendritic units (comprising
at least three linkage bonds), L represents the number of linear
units, and T represents the number of terminal units, as defined in
Hawker, C. J.; Lee, R. Frchet, J. M. J., J. Am. Chem Soc., 1991,
113, 4583.
[0027] In embodiments of the invention, the hyper-branched polymer
comprises the STOBA (self-terminated oligomer with hyper-branched
architecture), such as polymers prepared by polymerizing a
bismaleimide-containing compound with a barbituric acid.
[0028] The bismaleimide-containing compound comprises substituted
or unsubstituted bismaleimide monomer or substituted or
unsubstituted bismaleimide oligomer. For examples, the
bismaleimide-containing compound can be
##STR00001##
wherein n>1. In addition, at least one hydrogen atom bonded to
the carbon atom of the aforementioned bismaleimide-containing
compounds can be substituted optionally by fluorine, halogen atom,
cyano group, --R'', --CO.sub.2H, --CO.sub.2R'', --COR'', --R''CN,
--CONH.sub.2, --CONHR'', --CONR''.sub.2, --OCOR'' or OR, wherein
R'' can be selected from the group consisting of substituted or
unsubstituted C.sub.1-C.sub.12 alkyl group, thioalkyl group,
alkynyloxy group, alkoxy group, alkenyl group, alkynylene group,
alkenyloxy group, aryl group, alkylaryl group, heteroaryl group,
arylalkyl group, or combinations thereof. Further, the
bismaleimide-containing compound can comprise
##STR00002##
wherein R.sup.1 may comprise --RCH.sub.2-- (alkyl), --RNH.sub.2R--,
--C(O)CH.sub.2--, --CH.sub.2OCH.sub.2--, --C(O)--, --O--, --O--0--,
--S--, --S--S--, --S(O)--, --CH.sub.2S(O)CH.sub.2--, --(O)S(O)--,
--C.sub.6H.sub.4--, --CH.sub.2(C.sub.6H.sub.4)CH.sub.2--,
--CH.sub.2(C.sub.6H.sub.4)(O)--, diphenylene, substituted phenylene
or substituted diphenylene, R.sup.2 comprises --RCH.sub.2--,
--C(O)--, --C(CH.sub.3).sub.2--, --O--, --O--O--, --S--, --S--S--,
--(O)S(O)-- or --S(O)--. R may independently comprise hydrogen or
C.sub.1-C.sub.4 alkyl. The bismaleimide-containing compound may be
selected from the group consisting of
N,N'-bismaleimide-4,4'-diphenylmethane,
[1,1'-(methylenedi-4,1-phenylene)bismaleimide],
[N,N'-(1,1'-biphenyl-4,4'-diyl)bismaleimide],
[N,N'-(4-methyl-1,3-phenylene)bismaleimide],
[1,1'-(3,3'dimethyl-1,1'-biphenyl-4,4'-diyl)bismaleimide],
N,N'-ethylenedimaleimide, [N,N'-(1,2-phenylene)dimaleimide],
[N,N'-(1,3-phenylene)dimaleimide], N,N'-thiodimaleimide,
N,N'-dithiodimaleimide, N,N'-ketonedimaleimide,
N,N'-methylene-bis-maleinimide, bis-maleinimidomethyl-ether,
[1,2-bis-(maleimido)-1,2-ethandiol],
N,N'-4,4'-diphenylether-bis-maleimid and
[4,4'-bis(maleimido)-diphenylsulfone].
[0029] Further, the barbituric acid can be , or, wherein R.sub.1,
R.sub.2, R.sub.3 and
##STR00003##
R.sub.4 may be the same or different and comprise H, CH.sub.3,
C.sub.2H.sub.5, C.sub.6H.sub.5, CH(CH.sub.3).sub.2,
CH.sub.2CH(CH.sub.3).sub.2, CH.sub.2CH.sub.2CH(CH.sub.3).sub.2,
or
##STR00004##
[0030] STOBA (self-terminated oligomer with hyper-branched
architecture) can be prepared by polymerizing a
bismaleimide-containing compound with a barbituric acid or its
derivatives in solvent systems. In particular, the molar ratio of
the bismaleimide-containing compound and barbituric acid can be
20:1 to 1:5, preferably 5:1 to 1:2.
[0031] According to the present invention, the at least one
initiator employed is an agent, such as peroxide initiators or azo
initiators, which generates, upon activation, free radical species
through decomposition, and can be 2,2'-azobis(2-cyano-2-butane),
dimethyl 2,2'-azobis(methyl isobutyrate),
4,4'-azobis(4-cyanopentanoic acid),
4,4'-azobis(4-cyanopentan-1-ol),
1,1'-azobis(cyclohexanecarbonitrile),
2-(t-butylazo)-2-cyanopropane, 2,2'-azobis
[2-methyl-(N)-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide,
2,2'-azobis[2-methyl-N-hydroxyethyl)]propionamide,
2,2'-azobis(N,N'-dimethyleneisobutyramidine)dihydrochloride,
2,2'-azobis(2-amidinopropane)dihydrochloride,
2,2'-azobis(N,N'-dimethyleneisobutyramine),
2,2'-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamid-
e,
2,2'-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide),
2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],
2,2'-azobis(isobutyramide)dihydrate,
2,2'-azobis(2,2,4-trimethylpentane), 2,2'-azobis(2-methylpropane),
dilauroyl peroxide, tertiary amyl peroxides, tertiary amyl
peroxydicarbonates, t-butyl peroxyacetate, t-butyl peroxybenzoate,
t-butyl peroxyoctoate, t-butyl peroxyneodecanoate, t-butylperoxy
isobutyrate, t-amyl peroxypivalate, t-butyl peroxypivalate,
di-isopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate,
dicumyl peroxide, dibenzoyl peroxide, potassium peroxydisulfate,
ammonium peroxydisulfate, di-tert butyl peroxide, di-t-butyl
hyponitrite, dicumyl hyponitrite or combinations thereof.
[0032] In embodiments of the invention, the polymer with high ion
conductivity can be Nafion, sulfonated poly(ether ether
ketone)(s-PEEK), sulfonated polyimides (s-PI), phosphoric
acid/polybenzimidazole polymer (p-PBI), sulfonated poly(phenylene
oxide) (s-PPO), sulfonated poly(arylene ether sulfone) (s-PES),
sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (s-PPBP), or
combinations thereof.
[0033] The solvent used in the invention can be y-butyrolactone
(GBL), 1-methyl-2-pyrrolidinone (NMP), dimethylacetamide (DMAC),
N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO),
dimethylamine (DMA), tetrahydrofuran (THF), methyl ethyl ketone
(MEK), propylene carbonate (PC), water, isopropyl alcohol (IPA), or
combinations thereof.
[0034] It should be noted that the hyper-branched polymer can be in
an amount of 5-30 parts by weight, preferably 10-25 parts by
weight, based on 100 parts by weight of the hyper-branched polymer
and the polymer with high ion conductivity.
[0035] Moreover, in embodiments of the invention, the binder
composition for a membrane electrode assembly can further comprise
a conductive material, wherein the conductive material can comprise
organic conductive material, organic-inorganic conductive material,
inorganic conductive material, metal material, organic-metal
material, or inorganic-metal material, such as carbonaceous
material (Vulcan XC-72 for example), lithium-cobalt oxide,
lithium-manganese oxide, lithium-nickel oxide,
lithium-cobalt-nickel oxide, lithium-cobalt-nickel- manganese
oxide, or lithium-iron-phosphorus oxide. In some embodiments of the
invention, the binder composition for a membrane electrode assembly
can further comprise a catalyst, wherein the catalyst comprises
platinum, ruthenium, platinum-ruthenium alloy, platinum-tin alloy,
platinum-tungsten alloy, or platinum-molybdenum alloy.
[0036] Referring to FIGS. 2a and 2b, an adhesive layer 201,
consisting of the aforementioned binder composition, binds each
electrode 202 to a proton exchange membrane 203. The hyper-branched
polymer and the polymer with high ion conductivity of the binder
composition comprise the main configuration 204 of the adhesive
layer 201, and the conductive material 205 and the catalyst 206 of
the binder composition further blended, adhered, distributed,
and/or mounted with the hyper-branched polymer and the polymer with
high ion conductivity to build a linear-like structure (as shown in
FIG. 2a) or a network-like structure (as shown in FIG. 2b).
Therefore, the adhesive layer 201 exhibits air conduction, proton
conduction, electricity conduction, and water conduction due to
characteristic channels thereof, increasing the efficiency of the
cell.
[0037] For example, hydrogen gas reacts with the catalyst adhered
on the carbonaceous material of the adhesive layer 201 to produce
protons 207, as shown in following reaction formula:
H.sub.2.fwdarw.2H.sup.++2e.sup.-
[0038] The protons 207 move into the channels of the adhesive layer
201 via the proton exchange membrane 203, the electrons 208 move
into the channels of the adhesive layer 201 via cathode 202, and
incoming oxygen gas 209 reacts with the protons 207 and the
electrons 208 via the channels of the adhesive layer 201, producing
water. The reaction formula is shown below:
1/2O.sub.2+2H.sup.++2e.sup.-.fwdarw.H.sub.2O
[0039] Accordingly, the structure with a proton channel, provided
by the STOBA (as main component) and the polymer with high ion
conductivity (such as Nafion, sulfonated poly(ether ether
ketone)(s-PEEK), sulfonated polyimides (s-PI), phosphoric
acid/polybenzimidazole polymer (p-PBI), sulfonated poly(phenylene
oxide) (s-PPO), sulfonated poly(arylene ether sulfone) (s-PES),
sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (s-PPBP), or
combinations thereof), exhibits improved water retention ability,
chemical resistance, mechanical strength, thermal resistance,
flexibility, and proton conductivity, and prevents acid from
leaking out.
[0040] FIG. 3 is a partial schematic drawing of the main
configuration 204, illustrating the conduction mechanism of water
molecules and protons within the hyper-branched polymer (such as
the STOBA) and the polymer with high ion conductivity (such as the
s-PEEK).
[0041] The following examples are intended to illustrate the
invention more fully without limiting their scope, since numerous
modifications and variations will be apparent to those skilled in
the art.
Preparation of Hyper-branched Polymer
Examples 1-3
[0042] Bismaleimide-containing compounds, represented by
##STR00005##
were respectively dissolved in .gamma.-butyrolactone (GBL) and
reacted with barbituric acid represented by
##STR00006##
at 130.degree. C. for 6 hr, wherein the molar ratio of the
bismaleimide-containing compound and barbituric acid was 2:1 (with
a solid content of 20 wt %). By filtration and drying,
hyper-branched polymers (A)-(C) with DB of 50% were obtained.
Preparation of Binder Composition for a Membrane Electrode
Assembly
Example 4
[0043] The hyper-branched polymer (A) (having a solid content of 20
wt %, dissolved in GBL) was mixed with the s-PEEK (having a solid
content of 20 wt % and a degree of sulfonation of 67%, dissolved in
NMP). After stirring for 1 hr, the mixture was depressurized at low
temperature to expel air bubbles, obtaining the binder composition
(A), wherein the weight ratio of the hyper-branched polymer(A) and
the s-PEEK was 15:85.
Example 5
[0044] The hyper-branched polymer (A) (having a solid content of 20
wt %, dissolved in GBL) was mixed with the s-PI (having a solid
content of 3 wt %, dissolved in meta-cresol). After stirring for 1
hr, the mixture was depressurized at low temperature to expel air
bubbles, obtaining the binder composition (B), wherein the weight
ratio of the hyper-branched polymer(A) and the s-PI was 18:82.
Example 6
[0045] The hyper-branched polymer (A) (having a solid content of 20
wt %, dissolved in GBL) was mixed with Nafion 2020 (sold and
manufactured by E. I. Du Pont de Nemours & Co.). After stirring
for 1 hr, the mixture was left undisturbed for 5 days, obtaining
the binder composition (C), wherein the weight ratio of the
hyper-branched polymer (A) and Nafion 2020 was 10:90.
Characteristic Measurements of Adhesive Layers comprising the
Binder Composition
[0046] The binder compositions (A) and (B) were respectively coated
on a glass substrate and subjected to a baking process. For the
baking process, the coating was sequentially baked at 80.degree. C.
for 30 minutes, 100.degree. C. for 60 minutes, and 130.degree. C.
for 120 minutes. After cooling, the coatings were stripped from the
glass substrate, respectively obtaining adhesive layers (A) and (B)
with a thickness of 25 um.
[0047] The water retention ability of the adhesive layer (A)
(comprising the STOBA-SPEEK) was measured via TGA (therapeutic
goods administration) and the results are shown in Table 1:
TABLE-US-00001 TABLE 1 water retention contributions of the
STOBA-SPEEK and moieties thereof per unit weight STOBA --SO.sub.3H
PEEK BMI free water 0.1904 5.7614 -0.5438 -1.8956 (<100.degree.
C.) bound water 0.1429 -0.4771 0.0960 -0.0568 (100~200)
[0048] Note that the water retention contributions measured below
100.degree. C. was defined as the weight of free water, and the
water retention contributions measured between 100-200.degree. C.
was defined as the weight of bound water
[0049] As shown in Table. 1, the STOBA exhibited superior water
retention ability higher than --SO.sub.3H, PEEK, and BMI
(bismaleimide monomer) due to an intramolecular hydrogen bond
formation between the STOBA and water. Therefore, the membrane
electrode assembly employing the binder composition can be operated
at higher temperatures in order to increase efficiency.
[0050] The mechanical strength of the adhesive layer (A), the
adhesive layer (B), the Nafion 112 film, the s-PEEK film, and the
s-PI film were measured and the results are shown in Table 2.
TABLE-US-00002 TABLE 2 adhesive adhesive layer (A) layer (B) Nafion
(STOBA:s- (STOBA:s- 112 s-PEEK PEEK = 20:80) s-PI PI = 18:82)
thickness 54 25 42 26 26 (.mu.m) tensile 2.25 4.94 5.87 2.69 4.22
strength (Kgf/mm.sup.2) extension 103.3 5.48 5.28 5.00 6.37 (%)
[0051] As shown in Table 2, the adhesive layers (A) and (B)
exhibited superior tensile strength and extension than the s-PEEK
or the s-PI resulting from the addition of the STOBA. Therefore,
the membrane electrode assembly employing the binder composition
had increased mechanical strength.
[0052] The mechanical strength of the adhesive layer (A), the
adhesive layer (B), the Nafion 112 film, the s-PEEK film, and the
s-PI film were immersed in boiling water (100.degree. C.) for 120
minutes. After cooling, the dimensional changes thereof were
measured and the results are shown in Table 3.
TABLE-US-00003 TABLE 3 adhesive adhesive layer (A) layer (B) Nafion
(STOBA:s- (STOBA:s- 112 s-PEEK PEEK = 20:80) s-PI PI = 18:82)
.DELTA.L 17% X 5% 2.5% 3.75% .DELTA.W 3% X 10% 12% 0% .DELTA.T 12%
X 19% 53.9% 4.5% property soften- dissolution -- brittlement --
changes ing
[0053] Note that .DELTA.L represented the dimensional change in
length; .DELTA.W represented the dimensional change in width; and
.DELTA.T represented the dimensional change in thickness.
[0054] As shown in Table 3, the adhesive layers (A) and (B)
exhibited superior dimensional stability and overcame the
brittlement problems of the s-PI or the s-PEEK.
Measurement of Warpage and Adhesion
[0055] The binder composition (C) was respectively coated on one
side surface of first and second gas diffusion layers (carbon
paper) and two side surfaces of a proton exchange membrane
(comprising the STOBA, the s-PEEK, and the s-PI). Next, the proton
exchange membrane and the second gas diffusion layer were
sequentially disposed on the first gas diffusion layer. After hot
rolling, the above structure was respectively baked at 70.degree.
C. and 130.degree. C. for 15 minutes, obtaining a membrane
electrode assembly.
[0056] Next, the membrane electrode assemblies were respectively
immersed in water at 25.degree. C. for 15 hrs and at 100.degree. C.
for 1.5 hrs. After removal from water, the membrane electrode
assemblies were observed to contain no warpage or peeling.
[0057] Accordingly, the adhesive layers made of the binder
composition of the invention (STOBA & the s-PEEK or the STOBA
& the s-PI) exhibited higher water retention ability, and
mechanical strength than the layers consisting of the s-PEEK or the
s-PI. Further, the adhesive layers made of the binder composition
of the invention exhibited high dimensional stability when immersed
in boiling water due to the main component the STOBA. Therefore,
the adhesive layers made of the binder composition of the invention
exhibited minimal swelling and brittleness even when exposed to
100.degree. C. and 100% RH.
[0058] Moreover, in comparison with conventional Nafion 112, the
adhesive layers made of the binder composition of the invention
exhibit higher water retention ability and mechanical strength and
did not softened or become brittle. The adhesive layers of the
invention had an electrical conductivity of
1.times.10.sup.-2.about.5.times.10.sup.-2 S/cm at 25.degree. C.
similar to the Nafion film, and had an electrical conductivity of
1.times.10.sup.-15.about.5.times.10.sup.-1 S/cm at 120.degree.
C.
[0059] While the invention has been described by way of example and
in terms of preferred embodiment, it is to be understood that the
invention is not limited thereto. To the contrary, it is intended
to cover various modifications and similar arrangements (as would
be apparent to those skilled in the art). Therefore, the scope of
the appended claims should be accorded the broadest interpretation
so as to encompass all such modifications and similar
arrangements.
* * * * *